assorted beginner questions

This is a mixed bag. These are the questions that I
would ask an
informed friend. They might be obvious, but they are
not obvious
to me (yet, I hope).
-----------------------------
As I read code in Squeak, I discover method names that
I do not
know. How do you find these methods if you don't know
the type of
the receiver? For example,

    self subclassResponsibility.
-----------------------------
In the floor method from Number,

    truncation _ self truncated.

What does the underscore mean?
-----------------------------
I want to apply smalltalk to fibonacci numbers. I add
this method
to Integer,

fib:
    (self = 0) ifTrue: (^0)
    (self = 1) ifTrue: (^1)
    ^ (self - 1 fib) + (self - 2 fib).

Next, I would like to memoize this method, (because of
the
enormous performance gains).  I do not see how to
memo-ize things
in smalltalk. Can somebody help me see the necessary
shift in
thinking?

and

Would a smalltalker even take this approach?
-----------------------------

I am still waiting for things to >click< w/rt
smalltalk.  I know
that I don't know and that's all that I know :)

Thanks to all the people on this list for letting this
list be a
place where you can ask questions in this fashion w/o
the
certainty of abuse and dismissal.

Mark.


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On Tue, 02 Oct 2007 20:22:01 -0700, Mark Smithfield  
<[hidden email]> wrote:

> In the floor method from Number,
>
>     truncation _ self truncated.
>
> What does the underscore mean?

:=

In some images it shows up as a left-pointing arrow.

I'm not sure if that's coming back in later iterations or not.

I don't see why memoization would be different in Smalltalk. Or why it  
would specifically have to be, rather. You might create a Fibonacci class  
that contained an array or somesuch and cached the numbers that had  
already been called. (Slowly taking up more and more space over time.)
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Hi Mark,

Welcome to the list, and Smalltalk.

This is an error that a programmer uses to call attention to something that
another developer should have done.  In Smalltalk we have something called
inheritance.  This basically means that if you subclass an object the
subclass can be considered to have, or implement, all the methods of its
parent object.  There are times when you want the subclass to provide its
own content in a method but you want to make sure that all subclasses
provide a valid answer to the message.  In that case you implement the
method and have it call self subclassResponsibility.  Which would raise and
error that says, your class should have overridden this method, or something
like that.  This tells you that you made a mistake and should implement a
method with the same name.

For example:

A superclass named: StoreProduct
        Might implement a  
        StoreProduct class >> isTaxible
                "return a Boolean describing if product requires collecting
State Sales tax"
                ^self subclassResponsiblity

Then a subclass named: StoreProductFood
        Would override this method with
        StoreProductFood class >> isTaxible
                "return a Boolean describing if product requires collecting
State Sales tax"
                ^false

Another subclass named: StoreProductNonFood
        Would override this method with
        StoreProductFood class >> isTaxible
                "return a Boolean describing if product requires collecting
State Sales tax"
                ^self manufacturer hasStoreLocationIn: Store
currentLocationState.

Or something like that.

> -----------------------------
> In the floor method from Number,
>
>     truncation _ self truncated.
>
> What does the underscore mean?

 It is an assignment operator, it is much better to use :=

You need to create the method.  

The method can not have a : after it unless you are providing a argument to
your method

So you would leave that out, then find the template by selecting the
protocol in your integer browser (mathematical functions), add the following
and accept it.  This will save the method in the class Integer.

Integer >> fib
        "return the Fibonacci sum for the receiver"
        self > 0 ifFalse: [^0].
        self = 1 ifTrue: [^1].
        ^(self - 1) fib + (self - 2) fib

Then you can collect the sequence by doing something like:

        (1 to: 10) collect: [:i | i fib].

Highlight this and print it and get:

        #(0 1 1 2 3 5 8 13 21 34 55)

>
> and
>
> Would a smalltalker even take this approach?

Sure, it makes sense.

You are welcome.  

Ron Teitelbaum
President / Principal Software Engineer
US Medical Record Specialists
www.USMedRec.com

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Hi.


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